[AlanEdge]

It depends on your objectives.

If you take angel/institutional money, you should at least have a good idea of what billion-dollar-plus market you're going after.

How specifically you monetize within that market can't always be pre-determined because its a function of a really good product (which takes a lot of morphing/iteration).

It's not a good idea to bank on advertising (unless you're building an ad network) or unless you're product has a great context for capturing purchase intent (from which you can do some pretty killer lead-gen/affiliate).